Hydraulic device for driving piles

ABSTRACT

A hydraulic device for driving piles including a casing accommodating a striker with an anvil block, a hydraulic power cylinder, having a rod connected to the striker and a hydraulic directional control selector. A control unit is separated from the directional control selector and is secured on a housing of the power cylinder coaxially with the striker. The hydraulic directional control selector comprises two valves, each of which is provided with two pilot chambers, communication pairwise with each other. The first valve puts the head end of the power cylinder in communication with the rod end, and the second valve establishes communication between the head end and the return flow line.

TECHNICAL FIELD

The present invention relates to construction machines, and,particularly, to a hydraulic device for driving piles.

DESCRIPTION OF THE ART

Known in the art is a hydraulic device for driving piles, comprising ahousing, accommodating a striker mounted with a possibility ofreciprocating therein and interacting with an anvil block mountedcoaxially therewith in the housing (DE, A,2 900221). Mounted on thehousing coaxially to the striker is a hydraulic power cylinder whose rodis connected to the striker with its one end, whereas the other endthereof is connected to the piston which divides the hydraulic powercylinder into a rod end and a head end. The rod end is in constantcommunication with a pressure flow line. The head end through aspool-type hydraulic directional control valve alternativelycommunicates with a pressure flow line and a return flow line.

The control unit of the hydraulic directional control valve comprises apilot cylinder defined by the internal surface of the spool space whichcommunicates through a pressure relief valve with the return flow line,and a plunger mounted in this space and adapted for reciprocatingtherein, one end of the plunger interacting with the rod of the powercylinder.

The known hydraulic device for pile driving is highly reliable anddurable. However, in the structure disclosed the instant of reversal inthe lower position with respect to the instant of collision of thestriker and the anvil block cannot be exactly registered and adjusted,which makes the instant of switching with respect to the stroke positionunstable, and consequently, reduces the efficient use of the kineticenergy of the striker, and the effect of pile driving.

Moreover, the adjustment of the impact energy performed using additionalmeans, for instance, electromagnetic device for changing the strokelength of the accumulating cylinder piston, and therefore, volume of theaccumulating cylinder. This is done on command of the operator, that is,manually; this cannot provide an optimum energy impact for an adequateoperation of the device, which reduces its efficiency.

As is known, the spool-type systems require precision machining ofrather large surfaces of the members to be joined and are not adaptedfor use of low-viscosity liquids as a working fluid, such as, forexample, water, so as to avoid an inadmissible increase in leaks.

Moreover, the use of the spool-type directional control valve causes"short-circuiting" of power cylinders, that is, with the spool in adefinite position, the head end and the rod end of the power cylinderappear in communication with each other, which causes loss of theworking fluid and reduces the efficiency of the hydraulic drive by20-25%.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a hydraulic devicefor driving piles having such a structure of the directional controlselector that considerably increases the efficiency of the pile drivingoperation and renders it possible to use, as a working fluid,low-viscosity liquids, preferably water, while enhancing the efficiencyof the device.

The object of the invention is accomplished in a hydraulic device fordriving piles, comprising a housing accommodating, with a possibility ofreciprocating, a striker interacting with an anvil block coaxiallyarranged in the housing, and a hydraulic power cylinder installed on thehousing coaxially with the striker. The rod of the power cylinder isconnected with one its end to the striker, and with the other end, tothe piston which divides the hydraulic power cylinder interior into arod end which is in constant communication with a pressure line, and ahead end which is in alternating communication with the rod end and areturn flow line through a hydraulic directional control selector. Thecontrol selector has a control unit which comprises a pilot cylinderhaving its interior in communication with the return flow line through apressure relief valve, and a plunger installed in the interior of thepilot cylinder for reciprocating therein, which has one end interactingwith the power cylinder rod. The control unit is separated from thedirectional control selector and is secured to the casing of thehydraulic power cylinder coaxially with the striker, and the directionalcontrol selector comprises two valves, of which the first valve isadapted for bringing the head end of the power cylinder in communicationwith the rod end, and the second valve establishes communication betweenthe head end and the return flow line. Each valve has two pilot chamberscommunicating pairwise with each other, the first pair of the chambersclosing the first valve and opening the second valve being incommunication with the return flow line and, through a first controlvalve interacting at the end of the working stroke with the powercylinder piston, with the pressure line, whereas the second pair ofchambers, opening the first valve and closing the second valve,communicates with the interior of the pilot cylinder.

Provision of the pilot cylinder and the plunger which are separated fromthe directional control selector makes it possible to dispense with thespool-type directional control valve, and to employ the valve-typedirectional control selector whereby a low-viscosity working fluid canbe employed, for instance, water. The use of the valves as compared tothe spool-type arrangement of the state-of-the art device permits thepressure to be increased due to the absence of leaks, since the higherthe pressure, the tighter the valves are pressed in any extremeposition. The valves are changed over by virtue of a pilot pressurepulse. Thus, in the proposed device, the valves are changed over byvirtue of a pressure pulse in the pilot cylinder built up due to theaction of the power cylinder rod onto the plunger.

To ensure successive operation of the valves and eliminate their"short-circuiting", it is necessary that, in the first pair of chambers,the cross-sectional area of the first valve chamber is larger than thecross-sectional area of the second valve chamber, whereas in the secondpair of chambers, the cross-sectional area of the second valve chamberis larger than the cross-sectional area of the first valve chamber.

It is advisable that the pilot cylinder internal chamber be incommunication with the return flow line through a first throttleinstalled parallel to a pressure relief valve, and with the pressureline, through a second control valve interacting with the anvil block.

This structural arrangement permits the length of the striker workingstroke to be increased with each subsequent cycle and, at the same time,limits the maximum working stroke of the anvil block, which means thatif the amount of the pile driving exceeds that required in theoperation, the working stroke of the power cylinder piston isdiminished, whereby the impact energy decreases, and, on the contrary,as the pile resistance increases, the power cylinder develops the impactenergy to a maximum value. Thus, the impact energy depends on the piledriving depth per working stroke.

To prevent the hydraulic device from destruction, it is necessary toprovide an emergency valve adapted for interaction with the anvil blockand arranged parallel to the second pilot valve.

To make the change-over operation of the second valve slower and thusprevent the contacting surfaces from impact loads, it is expedient thatin the second pair of the chambers, the second valve chamber be broughtin communication with the pilot cylinder internal chamber through asecond throttle.

Advantageously, the inner end face of the pilot cylinder facing theinlet port is provided with a spring, the internal chamber of the pilotcylinder being brought in communication with the return flow linethrough a non-return valve.

This structural arrangement helps avoid collision of the hydraulic powercylinder head and the rod caused by the return stroke the rod, since thespring brings back the plunger of the pilot cylinder into a definiteposition, whereby the working fluid is sucked in from the return flowline through the non-return valve, thus preventing an increase of thepiston working stroke.

To bring down the pressure in the pilot cylinder internal chamber whenthe power cylinder operates for the working stroke, and consequently, toreduce metal consumption necessary for the members constituting thecontrol unit, and to render the operation of movable seals easier,preferably, the first pair of the pilot chambers be in communicationwith the return flow line through a third control valve whose pilotchamber communicates with the pilot cylinder interior space.

Advantageously, the hydraulic device is provided with a third throttleand a fourth control valve successively arranged and adapted for puttingin communication the first pair of the pilot chambers with the head endof the hydraulic power cylinder, the pi lot chamber of the fourthcontrol valve communicating through the first control valve with thepressure line.

This ensures a reliable change over of the hydraulic device to the"cocked-up position" (idle stroke) when driving piles in stiff soil, incases where, due to the striker rebound, the first control valve is openbut for a short period of time.

For a routine intervention into the automatic operation of the hydraulicdevice for driving piles, it is necessary to establish communicationbetween the pilot cylinder interior and the return-flow and pressurelines through an additional directional control selector mounted inseries with the first throttle.

The hydraulic device for driving piles according to the inventionfeatures the efficiency by 20-25% higher than that of a similar devicewherein use is made of a spool-type directional control valve, whichenhances the efficiency with the same drive power. The proposed deviceis ecologically pure, since used as a working fluid is water, sea waterinclusive, rather than mineral oil which is typical for the state-of-theart device. It is extremely important in view of the fact that thedevice is adapted for use in construction carried out in coastal areasand on the sea shelf, where environmental contamination is quiteundesirable or inadmissible. Moreover, provision is made in the proposedstructural arrangement of the hydraulic device for automatic adjustmentof the impact energy, which is also conducive to enhance the efficiencyof the pile driving, whereas the manual adjustment does not ensureoptimum impact conditions for pile driving. The device of the inventionis highly reliable in operation due to the provision of an automaticsystem for preventing emergency situations, which allows instantaneousreduction of the impact energy to minimum in cases where the drivingdepth exceeds the optimum value required, and also due to the fact thatit is insensitive to the working fluid pollution. The proposed device ischeaper in manufacture due to the improved technological effectivenesswhich does not require high precision machining.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

FIG. 1 illustrates a device for driving piles, according to theinvention, while in the initial position;

FIG. 2 shows a directional control selector, according to the invention;

FIG. 3 shows the moment of reversal in the pile driving device,according to the invention;

FIG. 4 is a view of FIG. 3, at the moment of re-reversal; and

FIG. 5 shows the manual operation of the pile device, according to theinvention, while in the initial position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The hydraulic device for driving piles, according to the invention,comprises a housing 1 (FIG. 1) which accommodates a striker 2 mountedwith a possibility of reciprocating and interacting with an anvil block3 coaxially arranged in the housing 1. Installed on the housingcoaxially with the striker 2 is a hydraulic power cylinder 4. A rod 5 ofthe hydraulic power cylinder 4 is connected to the striker 2 with itsone end, whereas the other end thereof is connected to a piston 6 whichdivides the interior of the power cylinder 4 into a rod end 7 and a headend 8. The rod end 7 is in constant communication through a pressureline 9, with a pump 10. The head end 8 communicates with a hydraulicdirectional control selector 12 through a piping 11, said directionalcontrol selector being adapted for establishing communication betweenthe head end 8 either with the rod end 7 or with a return flow line 13.

The hydraulic device is provided with a control unit 14 to effectmonitoring of the directional control selector 12, the control unitcomprising a pilot cylinder 15 and a plunger 16 reciprocatingly mountedtherein. The control unit is separated from the hydraulic directionalcontrol selector 12 and is essentially a quickly-detachable unit whichis fixed to a casing 17 of the hydraulic power cylinder 4 coaxially withthe striker 2, the pilot cylinder 15 being received by a bore 18 made ina kinematic pair, that is the rod 5--the piston 6, thus forming asliding sealed couple therewith. The bore 18 communicates with thesurrounding medium through a drain hole 19. One end face of the plunger16 interacts with the rod 5 of the power cylinder 4. To avoid collisionof the rod 5 and the head of the power cylinder 4, the interior end faceof the pilot cylinder 15 facing the inlet, is provided with a spring 20.

The hydraulic directional control selector 12 is made as two valves 21and 22, of which the first one is adapted for bringing the head end 8 ofthe power cylinder 4 in communication with the rod end 7, whereas thesecond valve 22 establishes communication between the head end 8 and thereturn flow line 13. The valves 21 and 22 have rods 23, 24, respectively(FIG. 2) with respective pistons 25, 26 and hydraulically operatedsprings 27, 28. The rods 23, 24 are smaller in diameter than valve seats29, 30, respectively, so that when in the closed position both valves21, 22 are held by a force equal to the product of a working pressure pby the difference between the cross-sectional area of the seat 29 (30)and the rod 23 (24). The pistons 25 and 26 divide the cylindersaccommodating them into pilot chambers 31, 32, 33 and 34 which are inpairwise communication with one another. The first pair of the chambers31 and 34 closing the first valve 21 and opening the second valve 22,communicates with the return flow line 13 (FIG. 1), and, through firstcontrol valve 35, which interacts at the end of the working stroke withthe piston 6of the hydraulic power cylinder 4, with the pressure line 9.The second pair of the chambers 32, 33 (FIG. 2) which open the firstvalve 21 and close the second valve 22, communicates with an interiorchamber 36 (FIG. 1) of the pilot cylinder 15.

To ensure successive operation of the valves 21 and 22 in the first pairof the chambers 31, 34 (FIG. 2), the cross-sectional area of the chamber31 of the first valve 21 is made larger than that of the chamber 34 ofthe second valve 22. In the second pair of the chambers 32, 33 thecross-sectional area of the chamber 33 of the second valve 22 is madelarger than that of the chamber 32 of the first valve 21.

An automatic change of the impact energy is effected due to the factthat the chamber 36 (FIG. 1) of the pilot cylinder 15 communicates withthe pressure line 9 through a second control valve 37, mounted in theanvil block section of the housing 1 with a possibility of interactionwith the anvil block 3, or with another movable member of the device,the chamber 36 of the pilot cylinder 15 communicating with the returnflow line 13 through a first throttle 38 mounted in parallel with apressure relief valve 39.

To avoid emergency situations, an emergency valve 40 is provided whichis mounted parallel to the second control valve 37 and is adapted forinteracting with the anvil block 3.

The contact surfaces of the valves 21, 22 are protected from impactloads by slowing down the change over of the second valve 22, which iseffected due to the fact that in the second pair of the chambers 32, 33(FIG. 2) the chamber 33 of the second valve 22 communicates with thechamber 36 (FIG. 1) of the pilot cylinder 15 through a second throttle41, whereas the first pair of the chambers 31, 34 (FIG. 2) communicateswith the pressure line 9 (FIG. I) and the head end 8, through a throttle44.

A maximum working stroke of the piston 6 of the hydraulic power cylinder4 is ensured by the fact that the chamber 36 of the pilot cylinder 15communicates with the return flow line 13 through a non-return valve 42.

To reduce pressure in the chamber 36 of the pilot cylinder 15 when thepower cylinder 4 is changed over to the "working stroke", and thus todecrease metal consumption of the members constituting the control unit14 and facilitate operating conditions of the movable seals, the firstpair of the pilot chambers 31, 34 (FIG. 2) of the valves 21, 22communicates with the return flow line 13 (FIG. 1) through a thirdcontrol valve 43 whose pilot chamber communicates with the chamber 36 ofthe pilot cylinder 15.

To adjust the operation rate and to ensure reliable operation of thevalves 21, 22 of the directional control selector 12, the first pair ofthe pilot chambers 31, 34 (FIG. 2) of the valves 21, 22 communicateswith the head end 8 (FIG. 1) through series-connected the third throttle44 and a fourth control valve 45, as well as with a hydraulicaccumulator 46. The pilot chamber of the fourth control valve 45communicates with the return flow line 9 through the first control valve35.

The hydraulic device for driving piles, according to the invention,operates as follows.

With the device in the initial position the device operates verticallyor close to that) the piston 6 with the rod 5 occupy the lowermostposition. Under the action of the hydraulically operated springs 27, 28(FIG. 2) the valves 21 and 22, respectively, are in the initial position(the valve 21 is closed and the valve 22 is open), whereby the head end8 (FIG. 1 ) of the power cylinder 4 is in communication, through thevalve 22 of the directional control selector 12, with the return flowline 13. The third control valve 43 and the fourth control valve 45 areclosed, whereas the first control valve 35 is open. The hydraulicaccumulator 46 is not charged.

The working pressure is delivered from the pump 10 and is appliedthrough the pressure line 9 to the rod end 7 of the hydraulic powercylinder 4 and to the hydraulically-operated springs 27, 28 (FIG. 2) ofthe valves 21 and 22 of the hydraulic directional control selector 12,thereby holding them in the initial position. Moreover, the workingfluid is supplied, through the first control valve 35 (FIG. 1), to thefirst pair of the pilot chambers 31, 34 (FIG. 2) of the valves 21, 22and thus causes the valves to assume the initial position (in case theyoccur, for some reason, in another position). The first valve 21 is heldin the closed position.

Under the action of the pressure in the rod end 7 (FIG. 1), the piston 6with the rod 5 start to moving upwards, thus forcing the fluid out fromthe head end 8 of the hydraulic power cylinder 4 through the secondvalve 22, to the tank, until the plunger 16 of the pilot cylinder 15thrusts against the bottom of the bore 18 in the rod 5. Then the rod 5,the piston 6, and the plunger 16 of the pilot cylinder 15 move jointlyupwards. In doing so, the plunger 16 of the pilot cylinder 15 forces thefluid located in the chamber 36 thereof to the second pair of the pilotchambers 32, 33 (FIG. 2) of the valves 21, 22, and to the pilot chamberof the third control valve 43.

As the pressure in said members rises, they start operating alternately.First, the third control valve 43 operates to bring in communication thefirst pair of the pilot chambers 31, 34 (FIG. 2) of the valves 21, 22and the return flow line 13 (FIG. 1). When a sufficient pressure rise isattained for the second valve 22 to operate, it isolates the head end 8of the power cylinder 4 from the return flow line 13. The piston 6,which continues its travel, compresses the fluid confined in the headend 8, which blocks the second valve 22 of the hydraulic directionalcontrol selector 12 in the closed position and acts upon the end face ofthe first valve 21. As soon as the total force of this pressure and thepressure in the chamber 32 (FIG. 2) of the first valve 21 reaches anadequate value, the first valve 21 operates to open, and brings incommunication the head end 8 (FIG. 3) with the pressure line 9 (i.e.,with the rod end 7).

The working fluid under pressure is admitted to the head end 8 of thepower cylinder 4 and blocks the first valve 21 of the hydraulicdirectional control selector 12 in the open position. It is due to thedifference between the areas (of the rod end and the head end) that thepiston 6 with the rod 5 is decelerated to a standstill. Thus, theworking stroke starts.

At the overtravel of the piston 6 of the power cylinder 4,the fluid isforced out from the pilot cylinder 15, through the pressure relief valve39 and flows to the return flow line 13.

In the course of the working stroke the piston 6 moves downwards andbecomes released from the plunger 16 which remains in the positionassumed during the upward travel of the piston 6. The pressure in thechamber 36 of the pilot cylinder 15 drops and the third control valve 43returns to the initial position under the action of the spring.

The re-reversal of the hydraulic directional control selector 12 takesplace when the first control valve 35 (FIG. 4) operates.

The piston 6, while moving downwards prior to the collision of thestriker 2 and the anvil block 3, interacts with the first control valve35, which consequently brings the pressure line 9 in communication withthe pilot chamber of the fourth control valve 45 and opens it, andthrough the third throttle 44, establishes communication with the firstpair of the pilot chambers 31, 34 (FIG. 2) of the valves 21, 22 to whichthe hydraulic accumulator 46 (FIG. 4) is connected.

Thus, said chambers 31, 34 (FIG. 2) of the directional control selector12 (FIG. 4) are simultaneously brought in communication with thepressure line 9 through the first control valve 35, wherein the workingpressure holds at that instant the fourth control valve 45 in the openposition. If with the piston 6 deflected the first control valve 35opens and the chambers 31, 34 (FIG. 2) of the valves 21, 22 remain underpressure, which ensures their changing over irrespective of the positionassumed by the piston 6 (FIG. 4) of the power cylinder 4.

After the hydraulic accumulator 46 has been charged to a definitepressure, the valves 21 and 22 operate alternately due to a differencebetween the cross-sectional areas of the first pair of the pilotchambers 31 (FIG. 2) and 34 of the valves 21 and 22, and also due todifferent blocking forces acting on the valves 21, 22. The hydraulicaccumulator 46 (FIG. 4) is discharged once the valves have been operatedin the following sequence: the third throttle 44--the fourth controlvalve 45--the second valve 22, and after the third control valve 43 hasoperated, directly through the latter.

It is by selecting the cross-sectional area of the third throttle 44 andthe capacity of the hydraulic accumulator 46 that there is monitored theinstant of changing over the first and the second valves 21 and 22 intothe position where the head end 8 (FIG. 1) communicates with the returnflow line 13, the change over rate of the second valve 22 being adjustedby the cross-sectional area of the second throttle 41.

An automatic mode of adjusting the impact energy is effected with theaid of the pressure relief valve 39 arranged in parallel with the firstthrottle 38. In this case, in the course of upward reversal, a portionof the fluid flows from the chamber 36 of the pilot cylinder 15 throughthe first throttle 38, with the result that with each cycle the plunger16 of the pilot cylinder 15 occupies the position higher than theprevious one, whereby the piston 6 with the rod 5 rises still higherwith each succeeding cycle, thus increasing the impact energy. This goeson until the hydraulic device reaches the maximum impact energy, or thedriving depth of a pile 47 gains the optimum value.

When operating under the conditions of maximum impact energy-, theplunger 16 of the pilot cylinder 15 compresses the spring 20, thusforcing the working fluid out from the chamber 36 of the pilot cylinder15. When the rod 5 along with the piston 6 moves downwards, the plunger16 actuated by the compressed spring 20 moves downwards under the actionof the spring 20, thus drawing in liquid from the return flow line 13through the non-return valve 42. The plunger 16 assumes a definiteposition and returns to this position after each cycle.

When the driving depth of the pile 47 per stroke reaches the optimumvalue, the second control valve 37 operates to feed a portion of thefluid into the chamber 36 of the pilot cylinder 15, and causes theplunger 16 of the pilot cylinder 15 to move downwards, whereby thepiston stroke and hence the impact energy decreases. Then the fluid isdrawn off again from the chamber 36 of the pilot cylinder 15, until thevolume of the drained fluid and that of the fluid supplied areequalized, which means that an optimum impact energy is established forthe given pile 47.

In case the driving depth of the pile 47 exceeds the permissible amount,the second control valve 37 operates together with the emergency valve40, and the chamber 36 of the pilot cylinder 15 is completely filledwith the working fluid, whereby the hydraulic device starts to operatewith a minimum impact energy.

The hydraulic device is provided with an additional hydraulicdirectional control selector 48 (FIG. 5) mounted downstream from firstthrottle 38 and bringing the chamber 36 of the pilot cylinder 15 incommunication with the return flow line 13 and the pressure line 9. Whenuse is made of a combined automatic and manual adjustment of the impactenergy, the operator can intervene in the operation of the device byvarying the impact energy, so as to increase or decrease it, ifrequired.

INDUSTRIAL APPLICABILITY

The invention can find most utility when used in coastal constructionworks and on the sea shelf where the environmental contamination isquite undesirable or inadmissible.

We claim:
 1. A hydraulic device for driving piles, comprising:a housingand a striker reciprocating within said housing; an anvil block disposedwithin said housing coaxially with said striker and adapted to contactsaid striker; a hydraulic directional control selector including (i) afirst valve with a first pilot chamber and a second pilot chamber, (ii)a second valve with a first pilot chamber and a second pilot chamber,and (iii) a control unit having a pilot cylinder and a plunger; ahydraulic pressure line, a return flow line and a pressure relief valve;a hydraulic power cylinder having a rod with a first and a second enddisposed on said housing coaxially with said striker; a piston disposedwithin said hydraulic power cylinder and separating said hydraulic powercylinder into a rod end and a head end, said rod end permanentlycommunicating with said hydraulic pressure line, said head endalternately communicating with said rod end and said return flow linevia said hydraulic directional control selector; said first end of saidrod being connected to said striker and said second end being connectedto said piston; said control unit being separated from said hydraulicdirectional control selector and mounted on said housing coaxially withsaid striker; said pilot cylinder having a chamber communicating withsaid return flow line via said pressure relief valve; said plungerreciprocating within said chamber and having an end for interacting withsaid rod; a first control valve interacting with said piston at an endof a working stroke of said piston; said first valve connecting saidhead end to said rod end; said second valve connecting said head end tosaid return flow line; said first pilot chambers (i) communicating witheach other, (ii) closing said first valve and opening said second valve,and (iii) communicating with said return flow line and said hydraulicpressure line via said first control valve; said second pilot chambers(i) communicating with each other, (ii) opening said first valve andclosing said second valve, and (iii) communicating with said chamber ofsaid pilot cylinder.
 2. The hydraulic device of claim 1, whereinsaidfirst pilot chamber of said first valve has a cross-sectional area whichis larger than a cross-sectional area of said first pilot chamber ofsaid second valve; and said second pilot chamber of said second valvehas a cross-sectional area which is larger than a cross-sectional areaof said second pilot chamber of said first valve.
 3. The hydraulicdevice of claim 1, comprising:a first throttle arranged in parallel tosaid pressure relief valve; and a second control valve for interactingwith said anvil block; said chamber of said pilot cylinder communicatingwith (i) said return flow line via said first throttle, and (ii) saidhydraulic pressure line via said second control valve.
 4. The hydraulicdevice of claim 3, comprising an emergency valve arranged parallel tosaid second control valve for interacting with said anvil block.
 5. Thehydraulic device of claim 3, comprisingan additional hydraulicdirectional control selector arranged in series with said first throttleand communicating with said pilot cylinder and said return flow line. 6.The hydraulic device of claim 1, comprising:a third control valve havinga pilot chamber communicating with said chamber of said pilot cylinder,said third control valve communicating with both of said first pilotchambers and said return flow line.
 7. The hydraulic device of claim 10,comprising:a second throttle communicating with said second pilotchamber of said second valve and said chamber of said pilot cylinder; afourth control valve having a pilot chamber communicating with saidhydraulic pressure line through said first control valve; and a thirdthrottle arranged in series with said fourth control valve; both of saidfirst pilot chambers communicating with said head end via said fourthcontrol valve and said third throttle.
 8. The hydraulic device of claim1, wherein said pilot cylinder includes an inner end face, an inletport, and a spring disposed on said inner end face facing said inletport;wherein said device comprises a check valve communicating with saidchamber and said return flow line.